Singleton variable turns empty after switching views - swift

Question

I made a singleton class to access my user's email from any other class for easy upload of data to cloud. I am able to print the email in the first view but when i try to access it in other views or come back to this view, it shows up as empty.
class SingletonAccount: NSObject {
static var shared: SingletonAccount = SingletonAccount()
var userEmail: String = "ABCD"
}
I also set the singleton to be initialised only in the appDelegate so that it could be shared among all the other classes.
class AppDelegate: UIResponder, UIApplicationDelegate {
var window: UIWindow?
var userAccount: SingletonAccount?
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
// Override point for customization after application launch.
userAccount = SingletonAccount.shared
return true
}
Below is the first view controller that appears on launch
weak var userAccount: SingletonAccount?
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
self.navigationController?.navigationBar.isHidden = true
print(userAccount!.userEmail)
}
override func viewWillDisappear(_ animated: Bool) {
super.viewWillDisappear(animated)
}
override func viewDidLoad() {
super.viewDidLoad()
let tap = UITapGestureRecognizer(target: self, action: #selector(LoginViewController.tapRegister))
let appDelegate = UIApplication.shared.delegate as! AppDelegate
userAccount = appDelegate.userAccount
self.registerLbl.addGestureRecognizer(tap)
// Do any additional setup after loading the view.
}

Answer 1

The benefit of a singleton is to have access to the same instance from everywhere.
Declaring a property in AppDelegate is pointless. Just get the mail address with
let email = SingletonAccount.shared.userEmail
And declare shared as constant. The description Singleton implies a constant.
static let shared = SingletonAccount()
And it's not necessary that the class inherits from NSObject, it's not even necessary that the singleton is a class.

Answer 2

you're declaring a new instance of userAccount in your view controller. if you have to use the var in appDelegate do
let appDelegate = UIApplication.shared.delegate as! AppDelegate
let aVariable = appDelegate.userAccount
i would just always use SingletonAccount.shared. Or define you singleton globally outside of the SingletonAccount class
let gSingletonAccount: SingletonAccount = SingletonAccount()
class SingletonAccount: NSObject {
var userEmail: String = "ABCD"
}